Smith & Wesson has joined a growing number of AR-15 manufactures offering rifles with gas-piston system operation instead of the AR-15's traditional direct gas-impingement mechanism. S&W M&P15 PS utilizes a design recently patented by Adams Arms that is manufactured at the S&W factory. There is also a 15 PS that is California approved. These guns also feature a 10 round fixed magazine, bullet button, short stroke piston operating system, 1-piece Op rod, adjustable & removable gas plug, 1-piece carrier, and a picatinny gas block. This item also features a Troy 7" modular quad rail handguard.